26 lines
809 B
Text
26 lines
809 B
Text
/-
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Copyright (c) 2016 Microsoft Corporation. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Author: Leonardo de Moura
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-/
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prelude
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import init.logic init.applicative
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set_option new_elaborator true
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structure [class] alternative (f : Type → Type) extends applicative f :=
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(failure : Π {A : Type}, f A)
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(orelse : Π {A : Type}, f A → f A → f A)
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attribute [inline]
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definition failure {f : Type → Type} [alternative f] {A : Type} : f A :=
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alternative.failure f
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attribute [inline]
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definition orelse {f : Type → Type} [alternative f] {A : Type} : f A → f A → f A :=
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alternative.orelse
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infixr ` <|> `:2 := orelse
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attribute [inline]
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definition guard {f : Type₁ → Type} [alternative f] (p : Prop) [decidable p] : f unit :=
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if p then pure () else failure
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